Hey I think I can help! My dad is from Rural America and My mom is a Fancy Lady from the Big City (it was a real scandal) so my sib and I are oddly bilingual in one language. In certain rural dialects "Old Man" (especially with a possessive adjective i.e. 'mine' 'her' 'your') is used to mean specifically a patriarch of the family to which a person belongs (which can be father or husband, as you said, but can apply to grandparents, stepparents, or other male relatives that fill that role) as in "my old man won't let me out tonight, but you best believe I'm goin' anyhow." It has a level of exasperated affection; there are many old men, but (for better or worse) this one is mine. ALTERNATELY, especially in the city, it can be a derisive description when used about a stranger; an old man is no one of import, or someone to be regarded with scorn. The first and most important trait you notice about him is that he is past his prime. "Sorry I'm late, some old man ahead of me in line was shouting at the barista." This makes it an extremely interesting phrase because if you use it on someone you know but have an undefined relationship with it is either a term of familial endearment or a dismissive insult.
(When it comes to writing Batfam, this has almost as much utility as the belts XD)
edit: whoops just realized somebody already answered this really well, my bad, I gotta learn to read those replies
Okay, can anyone explain the nuances of 'Old Man' to me?
Like, it's a way of teasing someone about ageing and the passage of time. It's both a slang for 'dad' AND 'boyfriend/husband.' It MIGHT be a way of referring to other authority figures??
I just ... I'm trying to sort out references used by the various Bats.
Dick and Damian use it for Bruce.
Bruce uses it for Alfred.
Are they alluding to the parental role these guys have? (Damian definitely is.) Just teasing them about ageing?
I'm pretty sure a 'my' in the front firmly drops it into dad territory. But how about a definite article? No article at all?
I didn't grow up with this phrase, and it is challenging me!